MIL-STD-1553 is military standard published by the United States Department of Defense that defines the mechanical, electrical and functional characteristics of a serial data bus. It was originally designed for use with military avionics, but has also become commonly used in spacecraft on-board data handling (OBDH) subsystems, both military and civil. It features a dual redundant balanced line physical layer, a (differential) network interface, time division multiplexing, half-duplex command/response protocol and up to 31 remote terminals (devices).
As shown in FIG. 1, a conventional MIL-STD-1553 bus system includes a dual-redundant MIL-STD-1553 bus 14, a bus controller 10, up to thirty-one remote terminals 12 (three remote terminals 12 are represented in FIG. 1), and an optional bus monitor 16. There is only one bus controller 10 in any MIL-STD-1553-based system, and it initiates all message communication over the bus. The bus controller 10 operates according to a command list stored in its local memory, commands the various remote terminals 12 to send or receive messages, and services any requests that it receives from the remote terminals 12. The bus controller 10 also detects and recovers from errors and keeps a history of errors. A remote terminal 12 can be used to provide an interface between the MIL-STD-1553 bus 14 and an attached subsystem. For example, in a tracked vehicle, a remote terminal 12 might acquire data from an inertial navigational subsystem, and send that data over the MIL-STD-1553 bus 14 to another remote terminal 12, for display on a crew instrument. Simpler examples of remote terminals 12 might be interfaces that switch on the headlights, the landing lights, or the annunciators in an aircraft.
When components are disconnected from the MIL-STD-1553 bus 14, or an equivalent bus, (resulting in an unterminated remote terminal, or open port), interference is created in the bus. For example, in the scenario where the bus 14 is used to communicate with stores on board an aircraft, such as ordinance (e.g., missiles) carried on an aircraft, and the ordinance is utilized (e.g., fired, dropped, etc.), there is a connector (previously connected to the missile) that is no longer connected to anything. As a result, signals sent down the bus 14 to this connector may propagate or reflect back along the bus 14 upon reaching the open connector, creating interference.
Conventionally, MIL-STD-1553 data bus systems are limited to a linear topology. In other words, a non-linear topology, such as a star topology or a parallel topology, is not compatible with a MIL-STD-1553 bus system. As a result, the MIL-STD-1553 system is not compatible, for example, with the use of a carriage system of deploying weapons in which a single carriage store interface (CSI) on the bus 14 is used to communicate with multiple weapons or a single CSI on the bus is used to communicate with multiple remote terminals 12. Thus, a one-to-more than one or a one-to-many connection topology is not compatible with the conventional MIL-STD-1553 system or its equivalents.
U.S. Pat. No. 8,542,719 Lassini et al., the disclosure of which is hereby incorporated by reference in its entirety, discloses a repeater coupled to a main bus that extends the bus system to elements outside of the linear topology. This extensibility includes enabling the repeater to be connectable to one or more remote terminals as well as a repeated bus. The repeated bus is configured in accordance with the same standard as the main bus, such as MIL-STD-1553. The repeated bus, like main bus, also can have remote terminals coupled to it. The repeater is configured to provide messages to each of the elements that are connected to the main bus through the repeater.
However, some ground-based and airborne applications that use networks such as MIL-STD-1553 require more than 31 devices to be connected to the network. An example of such an application is a high capacity stores management system where the bus controller must be able to independently address and communicate with a large number of munitions. Another example is a retrofit application where new equipment needs to be installed in specific aircraft locations served by a MIL-STD-1553 bus which would cause the bus to exceed the maximum number of RTs (31). While the repeater described above defines a mechanism that effectively expands the address space on the bus by extending the network topology thereby allowing the connection of more than 31 remote terminals on a MIL-STD-1553 bus system augmented with a repeated bus, it does not describe how the number of remote terminals connected to a single MIL-STD-1553 bus can be arbitrarily expanded while maintaining compatibility with the standard protocol.